The present invention relates to a radial tire for heavy duty vehicles, and more particularly to an improved reinforcing structure including a carcass and belt capable of reducing tire weight without deteriorating other tire performance characteristics, such as tire strength, durability and the like.
In general, radial tires for heavy-duty vehicles such as trucks, buses and the like are provided on the radially outside of a carcass with a steel breaker (A) composed of four plies A1-A4 of steel cords as shown in FIG. 6. As to the cord angles of the four plies, the plies are arranged so that the cords form a stiff triangular construction. Thus, the breaker is very rigid and the tire is provided with a required strength.
On the other hand, nowadays, in connection with environmental issues, especially air pollution control, resource saving, waste disposal and the like, automobiles tire manufacturers are required to reduce tire weight, materials and the like.
If the number of breaker plies is merely decreased, naturally, the rigidity and strength become insufficient, and the steering stability decreases. For example, if the breaker ply number is decreased to two, in order to obtain the above-mentioned required strength, it is necessary to increase the cord thickness and cord count in each ply, and the resultant breaker renders the tire weight heavier than ever against expectation. Furthermore, in such a breaker, as the rigidity difference between the breaker ply and the adjoining carcass ply becomes too large, separation failure is liable to occur and the high-speed durability decreases.
It is therefore, an object of the present invention to provide a heavy duty radial tire, in which the tire weight is reduced without causing a deterioration in the strength (plunger strength), steering stability, high-speed durability and the like.